Plastic Surgery Research Council
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PSRC 60th Annual Meeting
Program and Abstracts

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Biomechanical Comparison of Lag Versus Bicortical Screw Fixation in Metacarpal Fractures
Priya Lewis, BA, Benjamin Gerke, BS, Zachary Filip, MD, Serkan Inceoglu, PhD, Jane Dhillon, MD, Mark Martin, MD, DMD.
Loma Linda University, Loma Linda, CA, USA.

Purpose: The lag screw technique has become the standard for open fixation of oblique, spiral and condylar hand fractures. Compression is achieved by over-drilling the near cortex so the screw head will pull the near and distal fragments together. The potential for iatrogenic comminution is increased. Bicortical fixation achieves compression with bone clamps prior to fixation.
The purpose of this study was to biomechanically compare two types of fixation with cyclic loading to more accurately describe physiologic stress to the metacarpals.
Methods: Utilizing a porcine model, second metacarpals were dissected and isolated. Dorsal-distal oblique midshaft osteotomies were created to simulate diaphyseal fractures. The fractures were reduced and fixated with 2.0mm coarse pitch screws with bicortical (cohort I) or lag (cohort II) techniques. Each bone was fixed on the proximal end with the load applied distally. The bones were first loaded with cycles of 10 to 80 N for 5,000 cycles at 2Hz. The load was increased by 5N every 5,000 cycles until failure (Figure 1).
Results: Bicortical (N=5) and lag (N=7) samples were included in the analysis. The mean cycles to failure for cohort I was 15,356 and 20,672 for cohort II (Figure 2). Similarly, the maximum load at failure was 94N for cohort I and 99N for cohort II (Figure 3). These values were not found to be statistically significant.
Conclusion: Our preliminary findings suggest that bicortical and lag screw fixation is similar in efficacy when subjected to cyclic loading. This data has clinical relevance as traditional lag screw fixation is more technically demanding and is more time consuming than simpler, faster bicortical screw fixation. There may be an opportunity to reduce errors and complications and decrease treatment costs if bicortical screw fixation replaces traditional lag screw fixation in the common oblique metacarpal fracture.



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